Basically you need a truck mount (if you REALLY can not swing it go portable *shivers)
You need a good pre spray, this can be anything from a bridgepoint product to some local manufacturer. It should be a liquid with a ph around 9-10. By using a liquid with a lower PH you will be effective in more situations and won't have to worry about what kind of carpet you are using it on (how much wool carpet is there in australia? You may want to get something even lower on the PH scale if you will run into wool regularly)
You will need a booster for you pre spray, I would recomend some kind of citrusolve type product.
You will need spotting chemicals, citrus gel, solvent gel, liquid solvents, fels bar, maybe some enzyme spotter, some stain magic, some form of reducer (for red stains) maybe some urine booster for both spotter and pre spray.
You will need a good wand that is appropriately sized for your machine. If you go truckmount go with a nice high flow 8-12 flow 14 inch wand. If you go portable, use an appropriate sized wand for that situation. If you do go portable I have heard many people say that a rotary tool (rotovac 360i or something like that) helps a ton.
You will need air movers, carpet rakes, furntiure tabs, hoses, hand tools, pump up sprayers, hydroforce (if truckmount)
The list is sort of long, I know there is lots of stuff I have forgotten.